Sun and a consortium of other businesses are going to lower Blackbox self-contained computing facilities into a Japanese coal mine to set up an underground datacentre, using up to 50 percent less power than a ground-level datacentre.

The coolant will be ground water and the site's temperature is a constant 15 degrees Celsius (59 degrees Fahrenheit) all year, meaning no air-conditioning will be needed outside the containers. This reduces the energy required for the water chillers, used with surface-level Blackbox containers.

The group estimates that up to $9 million of electricity costs could be saved annually if the centre were to run 30,000 server cores.

Sun is working with eleven other companies, including Internet Initiative Japan - an ISP, BearingPoint, Itochu Techno-Solutions and NS Solutions. They will form a joint venture with Sun. NTT Communications and Chuo University are also involved.

The disused coal mine is located in the Chubu region on Japan's Honshu island. Sun will build 30 Blackbox self-contained datacentres containing a total of 10,000 servers (cores). This can be increased to 30,000 cores if there is the demand for it.

The containers will be lowered 100m into the mine and linked to power, water cooling and network lines via external connectors.

Sun has been developing its Blackbox concept for three years and a typical one has 250 servers mounted in seven racks inside a standard 20-foot shipping container. Sun says that With T-series processors, a single Blackbox can hold up to 2,000 cores, providing 8,000 simultaneous processing threads.

Such a subterranean datacentre will be easier to secure against unauthorised entry and terrorist attacks. The Blackbox containers are robust enough to withstand earthquakes, being capable of withstanding a quake of magnitude 6.7 on the Richter scale. The Nihonkai-Chubu earthquake shook the region in 1983.

The project has been initially costed at $405 million and the site should start offering datacentre services to public and private sector customers in April, 2010.